Binocular Microscopes 31 



sequently do not produce good effects. To test the mirror, 

 a piece of white paper should be placed upon the stage of 

 the instrument, which must be set horizontally, and light 

 from a lamp reflected by the concave mirror on this ; then, 

 by sliding the mirror up and down on the tailpiece, it can 

 quickly be seen if the focal point can be obtained upon the 

 paper. 



BINOCULAR MICROSCOPES. 



We have hitherto been treating principally of the 

 monocular microscope, and this, it must be understood, is 

 the only form that can be used for critical high-power work 

 in fact, the Continental firms as a rule do not make 

 binocular microscopes at all, regarding them as unneces- 

 sary. Two or three of them, however, make a binocular 

 eyepiece, which will be found described under the head of 

 eyepieces. The advantage of a binocular microscope is, 

 that both eyes can be employed simultaneously, saving the 

 strain on the vision which is apt to ensue through the con- 

 stant employment of the monocular microscope, and the 

 endeavour to see in the best manner the detail in the speci- 

 mens examined. We should recommend every user of the 

 monocular microscope to train himself to work with either 

 eye, keeping the one not in use open ; this will be found of 

 the very greatest service. The universally understood bino- 

 cular microscope is provided with a prism, designed by 

 Wenham, which admits of the light going up a direct tube, 

 and reflects light also into a second tube. By this means 

 objects can be seen more naturally than with the mono- 

 cular microscope, for the reason that stereoscopic vision is 

 obtained, and objects having a certain amount of depth 

 may be seen completely with the binocular microscope, 

 whereas with the monocular it would be necessary to focus 

 in successive stages through the entire depth. Especially 

 is this true regarding opaque objects, with low powers. 

 The stereoscopic binocular conveys an impression of the 



